This is subset of Eric W. Biederman's "Sysfs cleanups & taggeddirectory support" patchset[1] with the following modifications.

* fix-i_mutex-locking-in-sysfs_get_dentry patch is added at the top and #14-Don_t-use-lookup_one_len_kern and #15-vfs-Remove-lookup_one_len_kern are dropped. This is because #14 contained had a bug where it might created dentry/inode for an already deleted sysfs_dirent. I think it's benefitial to keep single lookup path.

* Rewrote simplify-sysfs_get_dentry patch and #08-Implement-__sysfs_get_dentry, #09-Move-sysfs_get_dentry-below-__sysfs_get_dentry and #10-Rewrite-sysfs_get_dentry-in-terms-of-__sysfs_get_dentry are omitted as __sysfs_get_dentry() isn't used by anyone.

* #16, 19-25 are omitted as it isn't clear yet how the tagged entry support will end up.